This powerful genetic tool is used for species identification, conservation and management, playing a key role in protecting these vulnerable marine predators from overexploitation.
A RIPPLE EFFECT
Sharks are vulnerable to overfishing because they usually have few offspring and take a long time to mature. This becomes a ripple effect that disrupts the balance of marine ecosystems. Worldwide, there is a high and increasing demand for shark meat, fins and liver oil (squalene). In Asian markets, the demand for shark products mainly comes from shark fin soup, a popular dish at celebrations.
In South America, the demand is driven by the consumption of shark meat. In addition, squalene is widely used in cosmetics. There is evidence it comes from threatened shark species, but the full scale of the liver oil trade is still unclear.
AN IMPORTANT TOOL
Shark DNA barcoding is a technique used to identify and differentiate shark species based on their genetic material, specifically by analysing short, standardised gene regions. This method has become an important tool in marine biology, ecology and conservation efforts, as it provides a reliable way to distinguish species, even from small tissue samples like fins or flesh, which is critical for identifying species caught in fisheries or sold in markets.
From various studies conducted on shark DNA barcoding, the top five most frequently encountered species are the milk shark (Rhizoprionodon acutus), silky shark (Carcharhinus falciformis), tope shark (Galeorhinus galeus), scalloped hammerhead (Sphyrna lewini) and great hammerhead (Sphyrna zygaena).
Sharks at a fish market
KEY ASPECTS OF SHARK DNA BARCODING
- DNA Barcoding PrincipleDNA barcoding works by sequencing a specific part of the genome that is different between species but similar within a species. In animals, a common gene used for this is the cytochrome c oxidase I (COI) protein, which is encoded by the MT-CO1 gene. This gene is stable across species, but has enough variation to act like a genetic “barcode” for identifying different species.2. Application in Shark SpeciesSharks are often difficult to identify by physical appearance alone, especially when only parts of the animal, such as fins, are available (as in the case of illegal finning). DNA barcoding helps researchers and enforcement agencies identify shark species accurately, even when physical features are missing.
3. Conservation Implications• Illegal Wildlife Trade
Shark DNA barcoding is instrumental in combating illegal fishing and the trade of endangered species like those listed under the Convention on International Trade in Endangered Species (CITES). It enables law enforcement to verify species composition in markets and ports.
• Bycatch Identification
Many sharks are caught as bycatch in commercial fisheries. DNA barcoding helps in identifying the species caught unintentionally, which is essential for better fisheries management.
• Biodiversity Studies
DNA barcoding helps researchers understand shark diversity, discover hidden species, study shark migration, and track population changes over time.
4. Challenges and Considerations• Genetic Diversity
Some closely-related shark species may have very similar COI barcodes, which can make it challenging to differentiate between them.
• Reference Databases
For effective barcoding, robust databases like BOLD (Barcode of Life Data System) need to be updated continuously with accurate shark DNA sequences to ensure new and lesser-known species are included.
• Food Labels
Vague terminology is used to describe pet food ingredients, for example, using generic terms like “ocean fish,” “white fish” and “white bait”. As a result, consumers cannot make informed and environmentally-conscious decisions, and unwittingly contribute to the overfishing of endangered sharks.
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